fn main() {}
fn get_one(arr: &[i32]) -> i32 {
    let mut res = 0;
    for &item in arr {
        res ^= item;
    }
    res
}
#[cfg(test)]
mod get_one {
    use super::*;
    #[test]
    fn get_one_01() {
        assert_eq!(get_one(&[1, 1, 2, 2, 4]), 4);
        assert_eq!(get_one(&[1, 1, 5, 2, 2, 6, 6,]), 5);
    }
}
